On the relationship between fluorescence and molecular geometry solvent-assisted formation of luminescent intramolecular exciplexes from anthronyl-substituted anthracenes

The fluorescence efficiency of 1′,2′-dihydro-spiro[anthracene-9(10H),3′-[3H]benz[de]anthracen]-10-one in 10 solvents of varying dielectric constant has been investigated. The observed exciplex luminescence is attributed to a solvent-assisted intramolecular charge-transfer interaction between the ground-state anthrone and excited-state anthracene moietis. The geometry of the exciplex is suggested to resemble that of a σ-π complex.     

Synthese von N-geschütztem Eledoisin (6–11)-Hexapeptid unter Verwendung von Proteasen als Biokatalysatoren

Papain and -chymotrypsin were used for the protease-catalyzed assembly ofBoc-protected eledoisin (6–11)-hexapeptide by (2+4)- and (3+3)-segment condensation, respectively, in aqueous-organic solvent systems. As C-components, chemically synthesizedBoc-protected peptide methyl esters were employed. The nucleophilic tetrapeptide amide was prepared by papain-catalyzed (2+2)-segment coupling, while theZ-protected C-terminal dipeptide amide could be obtained by -chymotrypsin- and thermolysin-catalyzed peptide bond formation. In addition, the influence of various reaction conditions, such as solvent composition, nucleophile concentration and reaction time, on the yield of theBoc-protected eledoisin (6–11)-hexapeptide was determined.

Abkürzungen: Es wurden die IUPAC/IUB-Regeln für Aminosäure- und Peptidderivate befolgt; vgl. Eur. J. Biochem.53, 1 (1975). Die verwendeten Aminosäuren hatten mit Ausnahme von GlycinL-Konfiguration.Boc=tetr-Butyloxycarbonyl-,Z=Benzyloxycarbonyl-,Ac=Acetyl-, –OMe=Methylester.     

Model studies on carboxypeptidase Y catalyzed peptide synthesis in an aqueous-organic two-phase system

Carboxypeptidase Y catalyzes in a biphasic system containing carbon tetrachloride and carbonate buffer the reaction ofZ-Phe-OMe and variousZ-andBoc-protected dipeptide methyl esters with Val-NH₂ and Leu-NH₂, respectively. This method has been applied to the synthesis of the corresponding N-protected tripeptide amides on a preparative scale. Using a substrate—nucleophile ratio of only 1:2 or 1:3 the peptide derivatives are obtained in yields of 56–97%.Abbreviations: IUPAC-IUB rules for peptides are followed, see Eur. J. Biochem.27, 201 (1972).Boc=tert-butyloxycarbonyl,Z=benzyloxycarbonyl,-OMe=methyl ester, HPLC=high performance liquid chromatography, TLC=thin layer chromatography,CPD-Y=carboxypeptidase Y.     

Molecular design of two sterol 14α-demethylase homology models and their interactions with the azole antifungals ketoconazole and bifonazole

Summary Sterol 14α-demethylase (CYP51) is one of the known major targets for azole antifungals. Therapeutic side effects of these antifungals are based on interactions of the azoles with the human analogue enzyme. This study describes for the first time a comparison of a human CYP51 (HU-CYP51) homology model with a homology model of the fungal CYP51 of Candida albicans (CA-CYP51). Both models are constructed by using the crystal structure of Mycobacterium tuberculosis MT-CYP51 (PDB code: 1EA1).The binding mode of the azole ketoconazole is investigated in molecular dynamics simulations with the GROMACS force field. The usage of special parameters for the iron azole complex binding is necessary to obtain the correct complex geometry in the active site of the enzyme models. Based on the dynamics simulations it is possible to explain the enantioselectivity of the human enzyme and also to predict the binding mode of the isomers of ketoconazole in the active site of the fungal model.     

Enzymatic peptide synthesis in frozen aqueous systems: Use of N-unprotected unusual acyl donors

-Chymotrypsin (EC 3.4.21.1) was used for catalyzing the reaction of various N-unprotected non-coded phenylalanine ester derivatives with H-Leu-NH₂ and H-Arg-NH₂ in frozen aqueous solution at −15 °C. Compared with reactions at room temperature, a significant yield increasing effect could be established. The kinetic parameters of ester hydrolysis show that most of the unusual acyl donors (compared with the coded phenylalanine methyl ester) are well accepted substrates for -chymotrypsin.     

SYNTHETIC CAROTENOIDS, NOVEL POLYENE POLYKETONES AND NEW CAPSORUBIN ISOMERS AS EFFICIENT QUENCHERS OF SINGLET MOLECULAR OXYGEN

Novel synthetic polyene polyketones and new synthetic capsorubin isomers were examined for their ability to quench singlet molecular oxygen (1O2) generated by the thermodissociation of the endoperoxide of 3,3'-(1,4-naphthylene) dipropionate (NDPO2). C28-polyene-tetrone (1) exhibits the highest physical quenching rate constant with 1O2 (kq = 16 x 10(9) M-1 s-1). For comparison, the rate constant for the most efficient biological carotenoid, lycopene (3) is kq = 9 x 10(9) M-1 s-1 and that of beta-carotene (5) kq = 5 x 10(9) M-1 s-1. The presence of two oxalyl chromophores at the ends of the polyene chain seems to enhance the 1O2 quenching ability in the C28-polyene-tetrone (1). C28-polyene-tetrone-diacetal (2) (kq = 9 x 10(9) M-1 s-1) and C40-epiisocapsorubin (4) (kq = 8 x 10(9) M-1 s-1) also have high 1O2 quenching abilities. Two carotenoids from plants, phytoene and phytofluene, were much less efficient, kq values being below 10(7) M-1 s-1. Due to the very high singlet oxygen quenching abilities, C28-polyene-tetrone (1), C28-polyene-tetrone-diacetal (2) and C40-epiisocapsorubin (4) may have potential use in preventing 1O2-induced damage in biological and non-biological systems.     

Peptide sequence prediction supported by correlation-associated networks in human cerebrospinal fluid

During the course of biosynthesis, processing and degradation of a peptide, many structurally related intermediate peptide products are generated. Human body fluids and tissues contain several thousand peptides that can be profiled by reversed-phase chromatography and subsequent MALDI-ToF-mass spectrometry. Correlation-Associated Peptide Networks (CAN) efficiently detect structural and biological relations of peptides, based on statistical analysis of peptide concentrations. We combined CAN with recognition of probable cleavage sites for peptidases and proteases in cerebrospinal fluid, resulting in a model able to predict the sequence of unknown peptides with high accuracy. On the basis of this approach, identification of peptide coordinates can be prioritized, and a rapid overview of the peptide content of a novel sample source can be obtained.     

Versuche zur Anwendung von Thermitase als Katalysator zur Knüpfung der Peptidbindung

The utility of thermitase, a thermophilic proteolytic enzyme fromThermoactinomyces vulgaris, as a catalyst for peptide synthesis has been studied using several N-benzyloxycarbonyl dipeptide esters as carboxyl components and Leu-NH₂ as nucleophile. Couplings were most successful with substrates containing Met, Leu, Ala, Phe, Tyr in P₁-position, and Val, Ala, Pro in P₂, whereas the substrates with Val, Ile, Pro in P₁ failed to couple.

     

Rotational excitation cross sections of para-H2 + para-H2 collisions. A full-dimensional wave-packet propagation study using an exact form of the kinetic energy

A full-dimensional quantum dynamical study of the rotational excitation in para-para H2 + H2 collisions using the potential-energy surface of Boothroyd et al. [J. Chem. Phys. 116, 666 (2002)] is reported. The multiconfiguration time-dependent Hartree algorithm is utilized to propagate wave packets and the cross sections for collision energies up to 1.2 eV are determined by a flux analysis through the interaction of the wave packet with a complex absorbing potential. Calculations for a collection of total angular momenta up to J = 70 are performed; the missing channels are obtained with a J-interpolation algorithm.